Cobpobation obi



Jan. 3,

s. H. MORTENSEN ALTERNATING CURRENT uo rofi Original Filed June 10, 19221'Patentgfl ,Jan. 8,1929. i

uNi EDfsTArEs PATENT-onion.

v SOREN H. MORTI ENSEN, OF MILWAUKEE, WIS CONSITT, ASSIGNOB TO'ALLIS-GHAL'MEBS MANUFACTURING COMP-ANY, or mmyvnnxnnfwrsoonsm; ACORPORATION 01? nnnewnn'n.

ALTERNA rrNG C RR NT Moron;

' i Application filed June 10,1922, Serial F0. 567,2 49. Renewed January24, 1925.

This invention relates in general to alternating current motors and hasparticular "relation to synchronous alternating current motors whereinclosed-circuit windings are utilized for improving the starting char-.acteristicsof the motor or' for preventing or limiting hunting oroscillations in the speed of the motor. v r

In the design and construction of alternatingcurrent motors embodying aclosedcircuit winding on an element acting asthe secondary of the motor,either for starting purposes only or for'both starting and normalrunning purposes, it is especiallydesirable'that the windingjbe ,of atype which insures the production of high: starting torque without toogreat current drawn from the supplyline and also the required runningtorque under conditions of maximum efficiency.

In view of the fact that synchronous alters nating current motors willnot start as such, under any considerableload, it has-been the practice-'.to provide such motors with a. closed-circuit winding on the directcurrent may'fulfill thesame function as a squirrelcage .winding onaninduction-motor, inasmuch as it produces a, starting tor uewhenalternating current is supplie to t e'stator of theimo'tor; and inaddition to this function, this winding will also act as a damperendeavoring to prevent' the motor from swinging or hunting with respectto "the primary field in the stator.-

Because the-design and construction of asynchronous closed-circuit,winding for motors which gives the best characteristics as to startingtorque, has the least effect in pulling the motor into synchronism andmaintaining the motor at synchronous speed against any tendency to huntoroscillate, the

.actual design of commercial types of synchronous m0t0rs has been =ve'rymuch of a compromiseyhich oflers only fair results in the matter of acombination of increased starting torque and improved damping eifects.This arises from the fact that .a relatively high resistance winding isdesired for the purpose of producing maximum starting torque, whereas awinding of relatively'low resistance is required in order to producemaximum damping effects and for pulling the motor into synchronismduring the starting .operation.

On comparison of the torque efiects of on -din'ary commercialforms ofsynchronous and induction motors during the starting operation, it isfoundthat, for the same input,

the torque of. thesynchronous motor may be greater than' that of theinduction motor up to about-50 percent of synchronous speed.

The torque'of the synchronous motor thenfalls off until at about .90percent of synchronous speed, it may not be half as greatas that of aninduction motor of the same rating. Beyond this point, the torque of thesynchronous motor becomes feeble in comparison with that of theinduction motor until about 92 'or 93 percent of synchronous speed isattainedand the motor is excited by direct current, when the torquerises abrupt] to full strength; It is 'customa'ry to spea of the torqueexerted in bringing the motor from this speed value (92 or 93 percent ofsynchronous speed) up to actual .synchronoustspeed as the ull in torque.

For general purposes, e better practice includes starting a s chronousmotor with the direct current eld winding short-circuited, preferablythrough a resistance, thus decreasing the possibility of destructiveeffects of induced highpotential in the winding. 'However, the. currentinduced in this closed-circuit direct current winding has a variabletorque producin 'thestarting operation, this torque veffect beingpositive, that is, assisting the starting, and variable for 'speeds ofthe motor up to substantially 50 percent of synchronous speed, and beinnegative and variable above this latterrspee The final probable-resultof this method of starting is a variable increase in the starting torquebeyond that due to the squirrel-cage windin alone, for speeds less than50 percent 0 synchronous speed and a variable decrease in. such torqueforspeeds above the latter value, this de-i effect during results inaccordance with this invention may crease in 'availabletorquenoticeable. in the region ofspeedapproximating -to 80 percent'ofsynchronous speed.

, This invention includes among, its, features, the utilization of thedesirable effects arising fromstartingwith the direct current,- fieldwinding of a synchronous motor shortcircuited, and at the same timepreventing or limiting any undesirable effects that might otherwisebedue. to this winding. 5 Useful be secured in a synchronous motorhaving a directcurrent field element'provided w th Q an auxiliary,closed-circuit winding, pref- 'erably in'the form of asingle'quirrelcage, composed. of end.connecting devices and. cross .barsthrough the. polar portions 'of the field 'element, these cross barsbeing of different j'resistances and'f reactances, the

general arrangement being such as to provide circuits of relatively highimpedance available at the lower speeds during starting and of relativellow resistance and whose ,axes are dispose at substantial angles, pref-'erably' right angles, to the axes of the adjacent direct currentwindings, so as to co operate with the latterto a considerable degree,for torquefproducing-purposes at the regions of s higher speeds duringthe starting operation, an greatly increasing the torque available ateed where, in.th'e ordinary de of sync ronous motors, there is onlyrelatlvel little torque available.-

gn In carrying out' t e broad principle of the invention,

the bars intermediate the low resistance bars resistance, hi

centers of fie d ,purpose of 7 fects without .150 starting torque,i inaddition to the low rehighly desirable results are secured 'where asingle squirrel-cage winding is-mounted on the field element of themotor, this windin including cross-bars of low resistance an highreactance in the edges or tips of the fie d-poles and. bars-of higherresistance and lower' rea'ctance intermediate the low resist ance barslocated adjacent:

sistance bars a jacent thetips of the poles,

. at the centers and tips'of the poles being of J relatively highresistance.

Itis an'ob'ect of this-invention to provide an alternating current motorof improved design and construction embodyinga closedcircuit'windingonone eleme'ntof the motor trical characteristics arranged in interlacedrelation.

It is a-further objectof. this invention to p rovide a synchrononsmotorof improved esign and construction and embodying a closed-circuitwinding on the direct current the tips of each ofthese' poles includinga and including cross bars of different elec 7 Lipoaeae fieldgelementofthe motorcapable of exerting maximum starting torque both at. standstilland at the higher speeds, while still capableof exerting maximum efiectin preventing hunting or oscillationslin speed. 5

- It is-a further object of this invention to provide an improved designand construction of synchronous motor of-this general char:

act-er embodying a closed-circuit windingon vthe direct current elementof the motor, this windingincluding 'cross-bars'oflow resistance andhigh reactance adjacent the ti-ps of field poles and cross-barsof'highe'r re- It is a further object of this invention to 'sistancenearer the centers of the field poles.

provide an improved design and construction,

of synchronous motor embodying a closedcircuit winding for the directcurrent element of the motor, this windin including, cross-bars oflowresistance a jacent the tips of the field poles and. adjacent-thecenters of the poles and cross-bars of higher gesistance intermediatethe low resistance ars.

These and other objects andadvantages are attained by this invention,various novel'feas tures of which will be apparent from'the descriptionand drawings, disclosin one-embodiment of such invention, and wi 1 beparticularly pointedout in the claims.

In the accompanying drawings:

Figure 1 ma partially sectional tal side elevation of a synchronousmotor (embodying features of this invention.

Figure 2 is a fragmental plan view of the upper side of the rotatingfield element of the motorof Fig 1.

Figure 3 is a fragmental view similar to fragmeni Fig. 1, showing -amodified arrangement/of the conductors of the closed-circuit winding.

Figure 4 isa view similar-to Fig. 3, showinga further modificatiom I Asdisclosed in the drawings, the stator 10 of the motor comprises asupporting frame carrying a laminated core which isslotted atits innerperiphery, a distributed alternating current winding 12, ordinarily ofthe p'olyphase type, being suitably held in position inthe slots bywedges or otherwise. The rotor 13 of the motor compr ses. a-spider'14,or other support carried by the shaft, and-a rim-like element 15. 'of mgnetic material which is included in the m' g 'netic circuit of therotor. A plurality of definiteolar portions intheform of spaced polesoordinary construction, preferably laminated, are secured to the rim :15,each radially efije nding body portion 16 and tips 17 adjacentthe polarface of the pole. A winding 18 is mounted-in operative position on eachof the oles, being held aga nst unpliant supportmg plates 19 locatedbeneath the pole tips, and, if desired,Ta't the relatively stilfsupporting plate 1-9 is, in the base of the pole. .The.

- ordinary design of synchronous motor, in t the formof an annularcollar about thepole and of metal of relatively low resistance,

siderable reactance;

primarily that it inay have a damper etlectduring operation of the motorat synchronous speed; However, in order to obtain maximum effectivetorque at the higher speeds during the starting operation, where thetorque is ordinarily relatively smallythe discontinuous, it. constructedof metal, or are constructed of substantially non-conduc tive material.

A closed-circuit winding 21 is disposed in operative position adjacentthe polar faces;

of the field pdles. This winding comprises" end connecting devices, inthe fornrof end rings 23, usually of brass and'each in a single piece ora plurality of united sections, and cross 'bars extending through theface portions-of the poles, as indicated being equidistant from theaxis. of the rotor,

and connected at their'ends, by riveting,

brazing, or otherwise, to the end rings, so

as to be securely united-in both a mechani-- cal and electrical mannerto, such rings." These cross bars extending through-the field poles areof different characters as to resist- 1 ance and, likewise, are ofdifferent reac tance because of their difi'erent arrangements'in thematerial of the poles.

' The bars24, located within or adjacent the Y pole tips 17 orcircumferential .;edges ofthe poles, are of copper or other low.resistance-j material, and are-preferably fully embedded in the materialof'thepoles, so as to,have con- Bars ,25 located be-. tween the two lowresistance bars 24 in the pole tips are of brass or other material whoseresistance is considerably higher than that of the bars 24. These bars25 are disposed in partially open slots, as indicated, to reduce thereactance of thebars The arrangement of conductors described is such asto ance and low reactance.

give the effect of a closed-circuit winding whose crossbars aresubstantially equidistant from the axis of rotation of the motor,- withthe bars 24 in the pole tips of relatively low resistance and highreactance and other intermediate bars of relatively high resist- All' ofthese interi mediate bars may be ofrelatively high re--- sistance, asindigate'd in Fig. 4, or, as shown: in Figs. 1 and 3, one or more bars26at or nearest to the center or axis of the pole, may be of copper orother low resistance material, and, as in the case of the bars 2 4:,-fullyembedded in the material of the pole so as to-have considerablerea1tance. The specificarrangements of Figs. 1 and 3 are especiallydesirable where maximum damp- 'i'ng effect is particularly desired inthe operation of the motor.

In starting a synchronous motor of'the character described, the startingaction is similar; I that ofaninduction motor, alternatingeuir'entbeing-applied to" the stator winding. Whilethe-rotor is atstand-stlll,

the frequencygfoi the current-induced inthe closedeircuitiwindingis thesame as that of the primary current. Hence, the reactance of the crossbars 24, and also the bar26, if t the latter is incorporated in; theclosed-circuit winding structure, which are ,substansupporting .collars19 aremade. electrically 'tially wholly surrounded'by the material. of

the poles, is a maximum, and thesebars carstantial torque-producingeffect on the rotor.

The combined torque-producin effect of, the.

low resistance bars and the hig er -resistance bars 2511s a frel'atlvelylarge one which may readil be approximately as'grea'tfas that of aninuetion motor of ordinary design of the same ratingas thesynchronous-motor. As the speed of the motor increases, the frequency ofthe secondary current decreases and, hence, the reactance of thesecondary:

circuit decreases. v .'I"he sp eed of the metor continues -.r1'se,;.ordinar1ly with moreorless decreasein available ftorque,: 'until thespeed reaches a value well toward'percent of'synchronous speed,the'exact value being dependent upon the resistance otthe closedispulled into synchronism.

circuit winding, at which time direct'currentisappliedto-the-field-winding and the motor' .uring the startingoperation, the annular collars 19, if continuous and of relatively lowresistance, and the closed-circuited direct current windings'surroundingthe poles have considerable current induced therein, andthese elementsproduce single-phase magnetic fields whose torque-producing eli'ectsvary from a maximum positive'va'lue to a unaximum negative value, thelatter efiect'occurring probably when the speed of the motor is from 60to 80 percent of synchronous speed. Due to the fact that the reactance'of the bars 24 decreases and the current flowing in these bars increasesas the speed of the motor increases, palrs of these bars, one on'each ofthe adjacent poles,

along with the 'connecting portions of the end rings, form lowresistance paths which produce magnetic fields whose axes are spacedsubstantially'90 degrees from the axes of the magnetic field produced inthe direct current poles by the windings thereabout. The result of thecurrent flowing in the several angularly' spaced short-cir'cuited pathsof the field element is the production of. a

polyphase magnetic field whosecomponents are these. two fluxes 90degrees apart. The

torque-producingefi'ectof thisflux is such as to greatly increase theavailable torque on the motor at'the higher speeds duringthe startingoperation,- beyond what would be present these low resistance windingelements' were omitted. A i

' Aside from the effect of increasing the available on theimotor atregions oispeek'l where the starting torque is'a 'minladditionaleffect-of serving as damper wind ings when the motor is'o'perating-atsynchronous, 1 speed. These 1- desirable efi'ects, arising most probablyfrom thefactthat ant-e and most advantageously located, 1 are secured inagmotor of the character described without -appreciable decrease in (thetorque available at-stand-still and the lower startin speeds.

n the modification shown in there j is" an interlaced arrangement madeup of a. "loiv resistance bar 26 at the centerof-the pole "and one lowresistance bar 24 at each of the pole tips',these.barsbeing of highreactance so as to insure a satisfactory torque-pro'du'c-l ing effectthereof at the: lower speeds. Be-.'

tween the low. resistance bars 24: and 26 are located high resistance,low reactance' bars 25, similar torthe bars of Fig 1. The use of oneormore low resistance bars at thece'nte'rs of the poles. is ordinarilydesirable where it is'desired that the winding I shall be capable ofprodu ing maximum damping effects, in the operatjio'n' ofthe 'motor. l yY.

In Fig; 4: is shown a further -modification of the arrangement of thecross-bars, of the closed-circuit winding. This winding issubstantiallythe same as that of Fig. 3,

the difference being that' the low resistance bar 26 at-the center ofthe pole in Fig. 3 is replaced by a high resistance, low reactance bar25 sim1lar to the other bars 25, dampin efi'ects being .securedsubstantially through the low resistance bars 241 located in-the pole-tips'.- The specific-arrangement disclosed in e, more desirable wherethe at-- winding associated with the=fielieleinent of the motor andincluding an-in'terlacedarrangement of-bars otdifierent resistances,

and preferably of different reactances, which permits the attainment ofmaximum torque during starting and maximum damping effect during runningat synchronous' speedi or any desired combination of the twoeffects,this combination of 'efiects' being'considerably beyond what has beenattainable infthe past with theknowntypes of closedcircuit winding onthe field element of the o0 motor.

It will be apparent that it. isnot desired that the invention' claimedbelimited to the exact details of construction'shownand described, forobvious modifications will 'ocour to a person skilled in the art,

- mum, these 103v" resistance bars have the these low resistance pathsareof high reactis 'isvclaimed a .de seu i" L 15A synchronous motor,element having definitepohrportmns, and

a closed circuit wi.'nd1ngf for said element-i .comprisingnend; con'n'ctingdevices adj acent said.vpolaflportlonsg 'ars-electro-mag:

1 2; Kim

n 'neti'cally associated rvvithi. said :=."p'olar per-4 tions' and.connected to" said endoonnectihg devices, bars adjacent the edges of-said-polar' portions being of highenreactance'than bars nearer thecenters'of Sflld'pQlaI portions."

" 2, A synchronous. motor, comprising an I elementhaving definite polarportions, and a closed-circuit winding fOi said elen1ent comprising endconnectingdevices adj aent said polarportions, and barsrpassing throughsaid polarportions and connected to 5 said end connecting devices,- barsadjacent -.-.the circumferential edgesof .said'pola'r Pertions being oflower resistance and higher] qreactance :than harsnearer the centers of'saidsp'olar portions.f. 1

9 43'. synchronous" niotorpconiprising an element having definite polarportions,. and

a cl'o'sedpircmt. winding. forxsaid element comprising'fbars passingthrough said-pola-r.

portions and located at Q substantially the same distance from -the-'axis of rotation of said motor, and end 'conneoting devices connected;to saidf bars," certain of said bars beingof higher resistance andlov'ver reactance T than=others of saidbars'. Y

.4. A synchronous motor, comprising an element having definite polar(portions, and: a

closedcircuit winding for sai element c'oin 'pri'singendcdnnectingdevices adjacent said polar portions, and bars passing through saidpolar portions and located at substantially the same distance from.the'axis of rotation of said motor and connected to said end connectingdevices, bars adjacent the edges of said polar portions being of lowerresistance i i and higher reactance than bars nearer the prising alicenters of said polarportions.

5..A synchronous; motor, com

,- element having definite (polar portions, and a combinedfstarting andamping winding for said motor including bars extending transverselythrough said (polar portions adjacentthe faces thereof an substantiallyequidistant from the axis of rotation of said motor,

and devices for 'interconnectingsaid'bars, V

certain of the bars-adjacent -the edges and the centers .ofsaid polarportions being of relatively low resistance, and bars interme-- diatesald center and ed e bars being I of higher, resistance than'sai centerand'edge -bars. :6. A-" synchronou s motpr, comprising an element havingdefinite polar portions, and

a combined starting and damping-winding for said motor including, barsextending transversely through said polar portions ad'- jacent' thefaces thereof and substantially 13 6;

accepts equidistant'from the axis of rotation of said motor,'anddevice's for interconnecting said bars, bars adjacent the edges andthe centers of said polar portions being of relative-- ly low resistanceand highreactancefarid bars intermediate said center and edge bars beingof higher resistance and lower react- V ance than said "center andedgebars. V

7.'A synchronous motor, comprising an element having definite,olarportions, and a combined starting and damping winding for said'motor including bars extending transversely through said polar portionsadjacent the faces thereof and substantially equidistant from the axisof rotation of said motor, and devices for interconnecting said bars,bars adjacent the edges ofsaid-polar transversely through said polarportions-ad jacent the faces thereof and substantially equidistant fromthe axis of rotation of said motor, and devices for interconnecting saidbars, certain of said bars being of relatively low resistance and hi hreactance and others of said bars bein o relatively high resistance, andbars 0 one class being disposed in interlaced relation with respect tobars of the otherclass.

a combined starting and damping winding for said ;motor including barsextending transversely through said' polar portions adjacent the facesthereofand substantially equidistant from the axis'of rotation of saidmotor, and devices for interconnecting said bars, certain of said barsbeing of relatively low resistance and hi h reactance and others of saidbars being 0 relatively high resist-Q ance and low reactance, and bars.of one class being disposed in interlaced relation with respect to,barsof the'other class. a

10. An alternating current synchronous motor comprising a core elementhaving-a winding. adapted to produce definite polar portions, and aclosed-circuit winding for said element comprising end connectingdevices, and bars electromagnetically associated with said 'polarportions and connected to said end connecting devices, bars adjacent thecenters of said p'olar portions being of lower resistance than barsnearer the edges of said polar portions.

11. An alternating current synchronous motor, comprising a rotary coreof magnetic material having a winding adapted to produce definite polarportions, conducting elements of relatively low resistance extendingtransversely through the'definite polar portions of said core and havingtheir corresponding. ends electrically interconnected, andotherconducting elements of higher resistance than fid first elementsandh'aving their-axes at. the same distance from the axis of rotation ofsaid machine as the axes of the conducting elements oi said first groupare disposed, the conducting elements of the second group'associat'edwith the several polar portions being spaced from and symmetricallydisposed at the sides of indi-' I vidua-lconductors of said first groupand electrically interconnected therewith at the ends thereof.

12. An alternating synchronous motor comprising a core element having awinding p adapted to produce definite polar portions, and closed circuitwinding elements for said core element comprising barselectromagnetically' associated with said polar portions andconstituting a plurality of short circuit member at points equidistantfrom the axis of rotation of said motor and having their corresponding,ends interconnected, bars paths of definite resistances, certain of saidnearest the olar centers of the field member Y being of su stantiallylower resistance than bars further away from said centers. I 9. Asynchronous motor, comprising an element having definite polar portions;and

ing a core of magnetic material providedwith slots, and a closed-circuitwinding t'herefor comprising a plurality of sets of conduoting elementshaving electrically dissimilar characteristics disposed in the slots"of' said' core and substantially equidistant from the axis of rotationthereof, individual conducting elements of one set being each disposedbetween a pair of symmetrically arranged conducting elements of theother set and spaced therefrom through the intermediary of magneticmaterial.

16. An alternating current motor, comprising a rotary core of magneticmaterial having conducting elements of relatively low resistanceextending transversely of said core"a.ndhaving their corresponding ends"e 5 the same distance from the axis ofrotation of said motor'as theaize's of the conducting elements. of said first group are disposed,pairs cf conducting 'elements'of thexsecond' 'Vidual conductors of saidfirst group group being eech spaced from symmetrically disposed ,atopposite sides of indiand electrically interconnected therewith'at theends thereof.

In testimony whereof, the signature of the inventor is affixed hereto. QSOREN H. MORTENSEN,

